gabrielwu's blog

By gabrielwu, 6 weeks ago, In English

If you are interested in participating in the Montgomery Blair Informatics Tournament (mBIT), which will be held online from 12:00-4:00 PM EST on Saturday, November 14 (11/14/20), please register at https://mbit.mbhs.edu/. The contest will be hosted on our personal servers at https://mbit.live/. All problems were written by the Montgomery Blair HS Computer Team, including 12tqian, gabrielwu, galen_colin, smax, meiron03, Blastman, czhang2718, and csytrn. Special thanks to balbit for spending hours test solving our hardest problems!

mBIT is split into two divisions: Standard and Advanced. Teams may choose which division to compete in. Standard division problems are roughly USACO Bronze to Silver difficulty, while Advanced division problems range from USACO Silver to Platinum. Most Standard problems could be found on a Div 3 contest or early on in a Div 2 contest. Advanced problems are more comparable to Div 1 (and more difficult Div 2) problems.

mBIT allows teams of up to 4 competitors! Anybody may compete, regardless of their age or country. There will be Amazon gift cards reserved for the top high school teams in both divisions, in addition to the top overall teams in the Advanced division (this means that non-high school teams in the Advanced division are eligible for prizes). To qualify for "high school status," all members of your team must be current high school (or middle school) students.

UPDATE: Problems, editorials, and results are available in this blog post.

Prizes (per person, subject to change):

  • $50, $25, $25 for the first, second, and third HS teams in Advanced

  • $25, $10, $10 for the first, second, and third overall teams in Advanced that are not among the top three HS teams

  • $25, $10 for the first HS team and first MS team in Standard

  • All prize winners will get an exclusive mBIT T-shirt (we can only ship within the US) and a Wolfram|Alpha Pro subscription (AoPS coupons for the MS team).

Here are the mBIT problems from our most recent contest in June:

All information, including problems from our contest last November, can be found on our website. Registration will remain open up until the day of the contest.

Message me or email mbit.organizers@gmail.com if you have any questions! We hope to see you compete!

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UPD: mBIT is now proudly sponsored by the amazing people at United Therapeutics, Wolfram Research, and Art of Problem Solving (AoPS)!

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5 weeks ago, # |
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I can't wait to participate!

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5 weeks ago, # |
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Cannot participate sadly, still from past contests I know its going to be fantastic, super excited to see what you guys have done!

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can't wait to get carried :)

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    5 weeks ago, # ^ |
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    omg im gonna get carried by u! calen golin orz is the best team!!

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5 weeks ago, # |
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Excited...!

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5 weeks ago, # |
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Looking forward to it!

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5 weeks ago, # |
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i’m so excited!! thank you for hosting :)

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5 weeks ago, # |
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Why did you guys change the name from rookie/varsity to standard/advanced?

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    5 weeks ago, # ^ |
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    Good question! The lower division may present a considerable challenge to many high school students -- even those who have many years of programming experience in school. We did not want the name "rookie" to discourage smart high school CS students who are newer to programming competitions, so we opted for the more neutral "standard" label. In particular, we did not want to have less experienced teams sign up for our advanced division, which can get very difficult.

    If you're unsure about which division to participate in, take a look at our previous contests and ask yourself which problems you would have more fun solving.

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      5 weeks ago, # ^ |
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      Thanks for the reply! What will be the scoring system for time penalty, wrong answer penalty, etc.?

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        5 weeks ago, # ^ |
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        There will be no penalty for multiple submissions. Rankings will be made strictly based on the number of points a team gets, with ties broken by the last submission on any problem. Read about our scoring system here: https://mbit.mbhs.edu/rules.

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5 weeks ago, # |
Rev. 3   Vote: I like it +27 Vote: I do not like it

Hi, I was solving 102802J - Cake Cutting in the Gym (from last November's mBIT), and don't understand Test 1 -- it seems inconsistent with the problem statement.

The problem states:

He is going to put a single candle in the cake

Each piece that doesn’t contain the candle has at most one side that does not have frosting

To me, this implies the candle will be inside the cake, but in Test1 the candle is outside the cake, and the judge answer is "0". Even if the candle could be outside the cake, I would argue the answer is still non-zero, because performing 0 cuts or 1 cuts still results in "all pieces have at most one unfrosted side", which is consistent with "all pieces without the candle have at most one unfrosted side".

12tqian, can you explain?

(At first, I thought maybe the TCs were randomly generated and the reference implementation happened to print 0 in this case, but then I saw the reference solution explicitly checks if the candle is outside the cake.)

Great contest though, and excited for this year's!

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    5 weeks ago, # ^ |
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    Hmm... Thank you for pointing this out! We've found our error -- our generator generates a random point inside the polygon with floating-point coordinates, then rounds the coordinates to long longs. In this case, rounding the point causes it to be just outside the polygon (which is not what we intended). The reason our original code had this check was because we originally intended for the point to be anywhere, but we decided having this extra condition didn't add anything to the problem.

    We should have either specified that points outside the cake should be answered with "0", or we should have ensured no test cases gave exterior query points. We are very sorry for this error, and we hope that no one encountered problems with this test case during the November 2019 contest (this problem ended up having 0 solves). AnandOza, if you would like to get past this test case 1, you can explicitly test for points outside the polygon or just check if the point is (6, 12) and print 0 (hopefully this exact same point doesn't appear in any other test).

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      5 weeks ago, # ^ |
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      Gotcha. Yeah, I added that check and passed (I looked at the test case using Coach Mode, haha). I was just curious how it happened.

      So the original problem statement said "if the candle is outside, print 0" somewhere, I guess?

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        5 weeks ago, # ^ |
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        I don't quite remember, but maybe we had a condition that said the candle must appear in at least one piece.

        Thanks for catching this! We will work hard to make sure the upcoming contest does not have errors like this.

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Can we get money transferred instead of amazon gift card?

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    5 weeks ago, # ^ |
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    Yes, we will be able to work something out if you can't take Amazon gift cards.

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      5 weeks ago, # ^ |
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      Can I work it with groups of more than 4 people the thing is I have a telegram chat and all of us usually share contest solutions during contest.

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        5 weeks ago, # ^ |
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        All of us usually share contest solutions during contest.

        Huh? :eyes: There aren't many contests for groups of more than 4 people, let alone groups at all...

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        5 weeks ago, # ^ |
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        Only up to four people are allowed on a team. Obviously, you are not allowed to share solutions during the contest with people outside of our team.

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Are teams outside of US eligible for prizes?

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Is it rated?

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    5 weeks ago, # ^ |
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    Yes, your team's performance on mBIT will be compared with its predicted seed to generate a rating delta, which will be applied to your CF rating.

    Spoiler

    Sarcasm. It will be unrated.

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      5 weeks ago, # ^ |
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      Only people above orange can understand that sarcasm.

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4 weeks ago, # |
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MikeMirzayanov, why does Codeforces only support teams of 1-3 when doing a virtual contest?

(Mentioning it in this blog post because this is a team contest for 4 participants per team.)

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4 weeks ago, # |
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Team "calen golin orz":

I wonder which user out of the 4 will carry

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4 weeks ago, # |
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Looks like we have a Diwali dhamaka on the cards.

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4 weeks ago, # |
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For mBIT, can we use library code, internet code, or any other resources? I know for some competitions they only allow you one book for resources or something, but I guess this might be difficult to enforce in this environment.

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    4 weeks ago, # ^ |
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    With respect to external resources, the mBIT rules are the same as the rules in a Codeforces contest. You may reference online (or in-print) resources and documentation, as long as it was published before the start of the contest. Of course, you can't ask for help online or communicate with anyone outside of your team during the contest.

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4 weeks ago, # |
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On 14 We have Diwali in India(one of the major festivals). and Timing for contest is 10:30 PM to 2:30 AM. But Still, See you guys on Leaderboard :)

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    4 weeks ago, # ^ |
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    Sorry about that! mBIT would normally be on the 21st but we moved it forward to avoid conflict with the TeamsCode Fall 2020 Online Contest. Moving the competition earlier in the day would be inconvenient for US students on the West Coast and make it more likely to overlap with a CF round.

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      4 weeks ago, # ^ |
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      Nah It's cool, You can't keep up with every country and its festivals lol. Looking forward to get carried xD!

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4 weeks ago, # |
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What versions of each language is used? For example, will there be access to C++17 64-bit (meaning can I use int128)?

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    4 weeks ago, # ^ |
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    We will be supporting Python/PyPy 3, Java 14, and C++17 with up-to-date versions of GCC on a 64-bit architecture, so 128-bit ints should work (I'm not 100% sure though).

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    4 weeks ago, # ^ |
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    By the way, none of our intended solutions use int128 (I don't know enough about it to know how much it helps), but I don't think you should need it to solve any of our problems.

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Will there be subtasks, or will everything be max tests?

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    4 weeks ago, # ^ |
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    We added some subtasks to prevent teams from getting completely stuck on the last few problems; where there are subtasks, the statement will specify what the additional constraints are and what fraction of the systests the subtasks will occupy.

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4 weeks ago, # |
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As a tester, I can confirm that some of the problems are solvable.

Also, Wolfram Alpha subscriptions will be provided to winners.

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3 weeks ago, # |
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Will the problem statements be available in other languages (like Spanish)?

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3 weeks ago, # |
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Super hyped for this :D

Will there be a live scoreboard for all the teams during the contest? And are the problems standard I/O (like CF) or more USACO-esque I/O?

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    3 weeks ago, # ^ |
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    Yes, there will be a live unofficial scoreboard during contest which will show the results of pretests. I/O is standard like CF.

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As a tester, I'm sure that you'll find many of the problems quite interesting and fun!

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mBIT starting in 10 minutes! Good luck to all teams :)

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Are we allowed to code at multiple machines at the same time?

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Are you having a server side issue, as my solution keeps on running on the test cases and is not showing the result. And the leader board page is also not opening

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    3 weeks ago, # ^ |
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    Yes, we're aware of it. We're working to fix it.

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Server Error (500) VERY SAD :(

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3 weeks ago, # |
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we couldn't submit in last 2 minutes

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Fun problems and overall high quality :)

When will the editorial be released?

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    3 weeks ago, # ^ |
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    We will release the editorial later tonight so people can discuss solutions first :). We're curious as to whether people have found alternative solutions to our problems. In the mean time, feel free to discuss!

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Will these be available on the CF gym soon?

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    3 weeks ago, # ^ |
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    Yep, after we finish system tests and scoreboards, which we estimate will be in around two hours (if all goes well :P).

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      3 weeks ago, # ^ |
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      can you guys please fix the link to the solution of the standard problem Plates. It hasn't been working since the editorial was published.

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        3 weeks ago, # ^ |
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        Not sure what you mean, it seems to be working fine for me. Are you sure you're using this editorial link?

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          3 weeks ago, # ^ |
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          Yeah but it got fixed just earlier. I decided to message gabrielwu since i was waiting for a while for the solution but nobody else noticed it. He was quick to fix it. Anyways, cheers!

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3 weeks ago, # |
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How to solve "Heating Rocks" from Standard section? Why my 2 pointer solution failed?

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    3 weeks ago, # ^ |
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    It's not always optimal to just split your array into two parts and have some rocks always in fireplace 1 and others in fireplace 2. Consider the case where T=2 and the initial values are 0, 0, 0.